Troubleshooting Serial Lines
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Notice that the interface buffers are listed at the end of the output. This
information can be useful to troubleshoot serial interface problems. It is
important to look at the number of free buffers. These numbers indicate the
memory that is available on the interface for buffering incoming and
outgoing packets.
debug serial interface Command
As always with debug tools, you must exercise caution. When executing a
serial debug or Frame Relay debug, the router can generate large amounts
of data that can encumber the router. Make sure that the specific command
is used when possible. debug can be used in conjunction with access lists
to focus the application of the debug tool.
The debug of a serial interface displays HDLC or Frame Relay communi-
cation messages. A sample follows that includes Frame Relay information. It
is important to understand that the output of this command varies with
the encapsulation type used on the interface:
Router_A#debug serial interface
Serial network interface debugging is on
Serial0(out): StEnq, myseq 135, yourseen 134, DTE up
Serial0(in): Status, myseq 135
Serial1(out): StEnq, myseq 2, yourseen 8, DTE up
Serial1(in): Status, myseq 2
Serial2(out): StEnq, myseq 247, yourseen 247, DTE up
Serial2(in): Status, myseq 247
Serial3(out): StEnq, myseq 30, yourseen 28, DTE up
Serial3(in): Status, myseq 30
Serial0(out): StEnq, myseq 136, yourseen 135, DTE up
Serial0(in): Status, myseq 136
Serial1(out): StEnq, myseq 3, yourseen 9, DTE up
Serial1(in): Status, myseq 3
Serial2(out): StEnq, myseq 248, yourseen 248, DTE up
Serial2(in): Status, myseq 248
Serial3(out): StEnq, myseq 31, yourseen 29, DTE up
Serial3(in): Status, myseq 31
Serial0(out): StEnq, myseq 137, yourseen 136, DTE up
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